There are a wide variety of display systems and apparatus which rely on the change of color for presenting a dynamic and colorful display. In the art of electric "writing" signs, for example, one common technique has been to use control of the sign's electrical power to "write-out" the sign as it is progressively illuminated from one end to the other. However, a disadvantage associated with this technique is that the sign is only one color, and may be only partially visibly illuminated at any one instant, unless there are multiple components which are separately illuminated.
Another technique is to employ two distinct signs arranged in strategically similar geometry and control their illuminations with respect to one another. The disadvantage of using dual placed signs is the complexity of the geometry involved and the complicated systems for attempting to "write-out" electrically either one of the two separate systems.
There are other systems which make use of different colored or differently illuminated liquids for providing a colorful visual display. For example, there are other devices which comprise an illuminable gas tube with a liquid pipe in overlapping or embracing relationship and a fluid circulating system for alternately flowing liquids of different colors through the liquid pipe. In these devices, the alternation is effected by multiple pumps and/or valves controlled by complex electro-mechanical mechanisms to effect the alternate flows. In other displays, such as ornamental fountains, light beams of different colors are played on the fountain sprays in different combinations and sequences to provide various ornamentation effects. The controls and lighting systems associated with such fountains are complex and costly and the visual effects of an illuminated spray is not the same as the visual effect provided by a spray where the liquid itself is colored.